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Module P7 Observing the

Universe

Lesson 2

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Summer Sky, Winter Sky

Orion visible in

December 

Orion not visible in

June

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Reminder Positions on the Earth are measured

using latitude and longitude.

For example, London has a latitude

of 51º 32¶ N and a longitude of 0º 5¶W. (Longitude is along  the equator)

(Note 5¶: = 5 minutes of arc = 5/60ths

of a degree)

See link for other cities

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From Earth, the stars

appear to be bright dots

fixed to the inside of a

giant ball or sphere.

This sphere is

completely imaginar y, 

but it is called ³the

Celestial Sphere´.

Celestial North Pole

Celestial South

Pole

Celestial Equator 

Ecliptic ± path of 

highest point of Sun

during a whole year 

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Declination is the

celestial equivalent of 

latitude. It gives you

the ³height´ in degreesabove the celestial

equator.

RA or right ascension

is the celestial

equivalent of longitude.It gives you the

³distance along´ the

celestial equator.

It would be sensible tomeasure it in degrees.

However , astronomers

measure it in hours

and minutes instead, 

with 24 hours

equivalent to 360º.